1. Field of the Invention
The present invention relates to an apparatus for detecting the positions at which respective wheels of a vehicle are mounted on the vehicle.
2. Description of the Related Art
A type of apparatus for detecting the positions at which respective wheels of a vehicle are mounted on the vehicle is known (for example as described in Japanese Patent No. 3212311), sometimes referred to as a direct type of wheel position detection apparatus. In this apparatus transmitter/receiver apparatuses (generally referred to in the following simply as transceivers) are attached to each of the vehicle wheels, with a tire pressure sensor also being attached to each wheel for directly detecting the inflation pressure of the tire that is mounted on the wheel. The term “wheel position” as used herein is to be understood as signifying, for example in the case of a four-wheel vehicle, a right-side front position, left-side front position, right-side rear position, or left-side rear position on the vehicle.
with the apparatus of Japanese Patent No. 3212311, a receiver apparatus equipped with an antenna is installed on the body of the vehicle. When a tire pressure detection signal obtained by a tire pressure sensor is converted to tire pressure data and transmitted by the corresponding transceiver, the transceiver also transmits ID information which identifies the transceiver. An apparatus installed on the body of the vehicle has data stored therein beforehand which relates the ID information of each transceiver to the position of the specific wheel to which that transceiver is attached (e.g., right-side front wheel, left-side front wheel, etc.). Thus, when tire pressure data are received from a transceiver via the receiver apparatus, it becomes possible to relate the tire pressure data to the specific wheel on which the tire is mounted.
In addition to determining the position of a wheel carrying a transceiver that transmits tire pressure data, the transceiver ID information also serves to distinguish transmissions of the transceivers of the vehicle concerned from transmissions that originate from transceivers of other vehicles.
However such a system has the basic disadvantage. That is, whenever an operation such as tire rotation is performed, the relationship between the respective transceivers and their wheel positions is altered. In such a case, it becomes necessary for a user to update the stored information that relates the ID information of each transceiver to the position of the wheel to which the transceiver is attached, in order to ensure that each transceiver remains correctly assigned to the correct wheel position in the stored data.
Hence there has been a requirement for a system whereby each transceiver can itself detect the position of the wheel to which it is attached, or whereby updating of the stored ID information can be performed automatically.
In view of this, the assignees of the present invention have previously proposed (in Japanese Patent First Publication No. 2007-015491) as system whereby each of respective triggering devices transmits a trigger signal at a fixed transmission signal strength, and each of the transceivers attached to the respective wheels detects the signal strength of a received trigger signal, using the detected signal strength value to judge whether the triggering device that transmitted the trigger signal is located relatively far from the corresponding wheel (i.e., the wheel to which the transceiver is attached) or relatively close to the corresponding wheel. In that way, each transceiver can automatically detect the wheel to which it is attached.
With such a type of automatic wheel position detection (autolocation), preferably a front wheel triggering device is used to transmit a trigger signal to be received by the transceivers that are respectively attached to the front wheels of the vehicle, while a rear wheel triggering device is used to transmit a trigger signal to be received by the transceivers that are respectively attached to the rear wheels.
With that method, the actual wheel position detection is executed by a processing unit that is installed on the body of the vehicle, i.e., that is coupled to a receiving apparatus which receives data transmitted from the transceivers that are attached to the wheels.
However in recent years it has become increasingly desirable to decentralize the processing of data as far as possible, allocating processing to peripheral units rather than to only one or more centralized units (i.e. ECU). In view of this, there is a requirement for a wheel position detection apparatus whereby all processing relating to wheel position detection is executed by the transceivers that are attached to the vehicle wheels, i.e., with each transceiver performing all of the processing required to detect the position of the specific wheel to which it is attached. The wheel position information can thereby be transmitted by each transceiver to a centralized apparatus (e.g., ECU).
It is an objective of the present invention to provide such wheel position detection apparatus.